If GarageBand for iOS won't open after updating to iOS 11

If GarageBand won't open after updating your iPhone, iPad, or iPod touch to iOS 11, turn off iCloud for GarageBand on your device.

Go to Settings > [your name], and tap iCloud.

Under "Apps Using iCloud," turn off GarageBand. You won't be able to access any GarageBand songs stored in iCloud Drive until this issue is fixed, but they won't be removed from iCloud. New songs will be saved to your device.